Technical Field
The present disclosure relates to a method for producing a heat sink that has a substrate and a heat radiating film formed on the surface thereof.
Background Art
Nowadays, electric circuits have been produced in a more compact size, and heat generation density has increased correspondingly. Therefore, an improvement in the heat radiation performance of electric circuits is one of the important challenges to be achieved.
An electric circuit with a large amount of heat generation has a housing, which is typically produced through aluminum die casting, for storing the electric circuit therein. However, although the thermal conductivity of metal is high, the rate of heat transfer of metal to the air tends to be low. For example, aluminum has a thermal conductivity of 100 W/mK, but has a rate of heat transfer (emissivity) to the air as low as about 0.1 to 0.3.
Herein, various attempts have been made to form a film of carbon, nitride, resin, or the like, which is a material with a high rate of heat transfer to the air, on the surface of a metal housing.
By the way, a heat sink is produced by casting a substrate using molding dies, taking the substrate out of the molding dies, transferring the substrate to a place where a coating operation is to be performed, and injecting resin onto the surface of the substrate, for example, to form a film thereon.
For example, JP S57-202683 A discloses a method for producing a heat radiating base for an electric heater, including die casting a substrate for the heat radiating base, and forming a resin covering layer on a surface to radiate heat of the substrate through resin injection molding using a mold, where the resin injection molding is performed while the substrate at a high temperature immediately after being die cast is placed in the mold.
According to the method for producing a heat radiating base for an electric heater described in JP S57-202683 A, a substrate at a high temperature immediately after being die cast is placed in a mold for resin injection molding, and a resin covering layer is formed on a surface to radiate heat of the substrate through injection of resin in such a state. Therefore, it is not necessary to additionally heat the substrate, and thus, a heat radiating base can be produced inexpensively and efficiently without using heating systems.